19,420 research outputs found
PVLAS experiment, star cooling and BBN constraints: Possible interpretation with temperature dependent gauge symmetry breaking
It is known that the kinetic mixing of photon and another U(1)_ex gauge boson
can introduce millicharged particles. Millicharged particles of mass 0.1 eV
can explain the PVLAS experiment. We suggest a temperature dependent gauge
symmetry breaking of U(1)_ex for this idea to be consistent with astrophysical
and cosmological constraints.Comment: 9 pages, 3 figue
Supersymmetric Electroweak Baryogenesis Via Resonant Sfermion Sources
We calculate the baryon asymmetry produced at the electroweak phase
transition by quasi-degenerate third generation sfermions in the minimal
supersymmetric extension of the Standard Model. We evaluate constraints from
Higgs searches, from collider searches for supersymmetric particles, and from
null searches for the permanent electric dipole moment (EDM) of the electron,
of the neutron and of atoms. We find that resonant sfermion sources can in
principle provide a large enough baryon asymmetry in various corners of the
sfermion parameter space, and we focus, in particular, on the case of large
, where third-generation down-type (s)fermions become relevant. We
show that in the case of stop and sbottom sources, the viable parameter space
is ruled out by constraints from the non-observation of the Mercury EDM. We
introduce a new class of CP violating sources, quasi-degenerate staus, that
escapes current EDM constraints while providing large enough net chiral
currents to achieve successful "slepton-mediated" electroweak baryogenesis.Comment: 35 pages, 9 figures; v2: several revisions, but conclusions
unchanged. Matches version published in PR
Dark Matter and Dark Radiation
We explore the feasibility and astrophysical consequences of a new long-range
U(1) gauge field ("dark electromagnetism") that couples only to dark matter,
not to the Standard Model. The dark matter consists of an equal number of
positive and negative charges under the new force, but annihilations are
suppressed if the dark matter mass is sufficiently high and the dark
fine-structure constant is sufficiently small. The correct relic
abundance can be obtained if the dark matter also couples to the conventional
weak interactions, and we verify that this is consistent with particle-physics
constraints. The primary limit on comes from the demand that the
dark matter be effectively collisionless in galactic dynamics, which implies
for TeV-scale dark matter. These values are
easily compatible with constraints from structure formation and primordial
nucleosynthesis. We raise the prospect of interesting new plasma effects in
dark matter dynamics, which remain to be explored.Comment: 14 pages, 6 figures Updated equations and figure
Gravitational Wave Burst Source Direction Estimation using Time and Amplitude Information
In this article we study two problems that arise when using timing and
amplitude estimates from a network of interferometers (IFOs) to evaluate the
direction of an incident gravitational wave burst (GWB). First, we discuss an
angular bias in the least squares timing-based approach that becomes
increasingly relevant for moderate to low signal-to-noise ratios. We show how
estimates of the arrival time uncertainties in each detector can be used to
correct this bias. We also introduce a stand alone parameter estimation
algorithm that can improve the arrival time estimation and provide
root-sum-squared strain amplitude (hrss) values for each site. In the second
part of the paper we discuss how to resolve the directional ambiguity that
arises from observations in three non co-located interferometers between the
true source location and its mirror image across the plane containing the
detectors. We introduce a new, exact relationship among the hrss values at the
three sites that, for sufficiently large signal amplitudes, determines the true
source direction regardless of whether or not the signal is linearly polarized.
Both the algorithm estimating arrival times, arrival time uncertainties, and
hrss values and the directional follow-up can be applied to any set of
gravitational wave candidates observed in a network of three non co-located
interferometers. As a case study we test the methods on simulated waveforms
embedded in simulations of the noise of the LIGO and Virgo detectors at design
sensitivity.Comment: 10 pages, 14 figures, submitted to PR
The Problem of Inertia in Friedmann Universes
In this paper we study the origin of inertia in a curved spacetime,
particularly the spatially flat, open and closed Friedmann universes. This is
done using Sciama's law of inertial induction, which is based on Mach's
principle, and expresses the analogy between the retarded far fields of
electrodynamics and those of gravitation. After obtaining covariant expressions
for electromagnetic fields due to an accelerating point charge in Friedmann
models, we adopt Sciama's law to obtain the inertial force on an accelerating
mass by integrating over the contributions from all the matter in the
universe. The resulting inertial force has the form , where
depends on the choice of the cosmological parameters such as ,
, and and is also red-shift dependent.Comment: 10 page
Random transition-rate matrices for the master equation
Random-matrix theory is applied to transition-rate matrices in the Pauli
master equation. We study the distribution and correlations of eigenvalues,
which govern the dynamics of complex stochastic systems. Both the cases of
identical and of independent rates of forward and backward transitions are
considered. The first case leads to symmetric transition-rate matrices, whereas
the second corresponds to general, asymmetric matrices. The resulting matrix
ensembles are different from the standard ensembles and show different
eigenvalue distributions. For example, the fraction of real eigenvalues scales
anomalously with matrix dimension in the asymmetric case.Comment: 15 pages, 12 figure
Fludarabine as a cost-effective adjuvant to enhance engraftment of human normal and malignant hematopoiesis in immunodeficient mice
There is still an unmet need for xenotransplantation models that efficiently recapitulate normal and malignant human hematopoiesis. Indeed, there are a number of strategies to generate humanized mice and specific protocols, including techniques to optimize the cytokine environment of recipient mice and drug alternatives or complementary to the standard conditioning regimens, that can be significantly modulated. Unfortunately, the high costs related to the use of sophisticated mouse models may limit the application of these models to studies that require an extensive experimental design. Here, using an affordable and convenient method, we demonstrate that the administration of fludarabine (FludaraTM) promotes the extensive and rapid engraftment of human normal hematopoiesis in immunodeficient mice. Quantification of human CD45+ cells in bone marrow revealed approximately a 102-fold increase in mice conditioned with irradiation plus fludarabine. Engrafted cells in the bone marrow included hematopoietic stem cells, as well as myeloid and lymphoid cells. Moreover, this model proved to be sufficient for robust reconstitution of malignant myeloid hematopoiesis, permitting primary acute myeloid leukemia cells to engraft as early as 8 weeks after the transplant. Overall, these results present a novel and affordable model for engraftment of human normal and malignant hematopoiesis in immunodeficient mice
Theory of quantum dot spin-lasers
We formulate a model of a semiconductor Quantum Dot laser with injection of
spin-polarized electrons. As compared to higher-dimensionality structures, the
Quantum-Dot-based active region is known to improve laser properties, including
the spin-related ones. The wetting layer, from which carriers are captured into
the active region, acts as an intermediate level that strongly influences the
lasing operation. The finite capture rate leads to an increase of lasing
thresholds, and to saturation of emitted light at higher injection. In spite of
these issues, the advantageous threshold reduction, resulting from spin
injection, can be preserved. The "spin-filtering" effect, i.e., circularly
polarized emission at even modest spin-polarization of injection, remains
present as well. Our rate-equations description allows to obtain analytical
results and provides transparent guidance for improvement of spin-lasers.Comment: 7 pages, 3 figure
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